Textbooks often consist not only of textual information but also of supplementary information. In this study, we investigated whether the comprehension and accessibility of supplementary information differs when it is placed around the text or inserted into the text. 81 university students were asked to read texts with supplementary information around the text and texts with supplementary information inserted into the text, and to answer questions related to the content. They were asked to answer questions about the content. They were also asked about their reading skills and the ease with which they could understand each text. The results showed that comprehension scores were higher when additional information was inserted into the text. In addition, only participants who think they are poor readers rated the supplementary information as easier to understand and remember when it was inserted into the text. Based on these results, the better layout of the textbook was discussed.